Peel and finely dice the onions. Clean, wash and halve the cauliflower. Cut the florets of one half into small pieces. Dice the stalk roughly. Heat the oil in a large pan. Fry the minced meat in it until crumbly.
Season vigorously with salt and pepper. Add onions, cauliflower florets and the diced stalk and fry briefly. Add cream and 300 ml water, bring to the boil. Stir 2 tbsp. starch and 5 tbsp. water until smooth, thicken sauce with it.
Stir in the mustard. Season to taste with salt, pepper and Worcester sauce.
For the base, finely chop the 2nd cauliflower half in portions in the universal chopper. Grate cheese finely. Peel, wash and roughly grate the potatoes. Grate the potatoes well with your hands.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Grease a tart mould with a lifting base (28 cm Ø) and sprinkle some breadcrumbs over it. Knead cauliflower, half of the cheese, potatoes, 75 g starch, 50 g butter, egg, salt and pepper.
Pour the mixture into the mould, press on the bottom and pull up a small rim (the mixture sticks a little).
Sprinkle the cauliflower base with 3-4 tbsp. breadcrumbs. Spread the chopped cauliflower mixture on top. Sprinkle with remaining cheese. Bake in the hot oven for about 50 minutes on the bottom shelf. If necessary, cover with aluminium foil about 10 minutes before the end of the baking time.
Wash and chop the parsley. Remove the tart, let it rest for about 10 minutes. Remove from the tin and serve. Sprinkle with parsley.